The present invention relates to a system for injection molding plastic materials using injection nozzles, especially valve gated nozzles including a hot runner system.
Hot runner mold nozzles have been used in many molding applications. There are several design elements included in valve gated nozzles including the method of operation, the design configuration of the gate when opened, the temperature control of the components adjacent the mold cavity and how leakage of the plastic is controlled.
Temperature control of the plastic adjacent the mold cavity represents a particular problem.
The heating and/or cooling of the nozzle stem is shown in U.S. Pat. Nos. 4,125,352, 4,406,609, 4,521,179 and 4,276,015. However, the methods used either heat or cool. The references do not teach how both heating and cooling can be achieved in the stem at different points in the cycle. The '352 and '609 references both relate to a valve stem containing a heat pipe, which can of course be used for both heating and cooling; however, there is no disclosure in these references either about how this would be done. The reason both heating and cooling is useful is for example heating would be used to quickly bring the stem to operating temperature from room temperature when the system was being started and cooling would be used to maintain the stem at operating temperature during the operating cycle.
Accordingly, it is a principal object of the present invention to provide an injection molding apparatus which enables close control of molten plastic temperature adjacent the mold cavity.
It is a still further object of the present invention to provide an apparatus as aforesaid which enables one to selectively heat or cool the molten plastic adjacent the mold cavity, especially in an injection nozzle or valve stem thereof.
Further objects and advantages of the present invention will appear hereinbelow.